The current method for forming a three-dimensional micropattern on the molding tool surface involves the formation of a stereo-micropattern on a photosensitive material by exposure. Subsequently, an electrically-conductive layer is formed on the patterned photosensitive material by a low-temperature vapor deposition or a silver plating before nickel or copper is electroplated to form the mold. However, the depth of the micropattern formed is often less than 0.15 .mu.m in view of the residual stress when the electroplating is carried out by a sulfamate nickel plating method. On the other hand, an electroless nickel method is not a workable substitute for the above-mentioned electroplating method on the grounds that the electroless nickel method must be carried out at a relatively high temperature of 90.degree. C., and that the photosensitive material and the substrate material are different from each other in heat expansion coefficient. Such problems can be technically overcome by a process in which the patterned photosensitive material is transferred to a silicon or glass substrate to form an unitary material by the dry or wet etching method before the electroless nickel method is executed. However, such a remedial measure as described above can complicate the entire method.
The embossing method disclosed by McGrew in the U.S. Pat. No. 5,521,030 was found by these inventors of the present invention to be inapplicable to the formation of the micropattern on the surface of a steel substrate by reactive ion etching, which was carried out under the conditions as follows:
1. Radio frequency (RF) power, 120 watts; reaction chamber pressure, 30 mTorr; and introduction of CF.sub.4 gas at the flow rate of 36 SCCM and oxygen gas at the flow rate of 4 SCCM.
2. RF power, 120 watts; reaction chamber pressure, 40 mTorr; and introduction of CF.sub.4 gas at the flow rate of 36 SCCM and argon at the flow rate of 4 SCCM.
3. RF power, 120 watts; reaction chamber pressure, 30 mTorr; and introduction of SF.sub.6 gas at the flow rate of 40 SCCM.
4. RF power, 150 watts; reaction chamber pressure, 40 mTorr; and introduction of argon at the flow rate of 20 SCCM.